Charles Darwin may have just lost Evolution Exhibit A, otherwise known as Archaeopteryx

For nearly 150 years, dino boffs have been wagging their fingers at each other in a war over whether the winged Archaeopteryx deserves to be venerated as the first bird.

Most of them were happy to go along with the theory that Archaeopteryx sat squarely at the root of the broad group of proto-birds, known as Avialae, from which our modern feathered friends have emerged.

The emblematic creature was also held up as a case study of evolutionary transition, to wit, from dinosaur to bird.

And not just any old case study — Archaeopteryx's apparent role as evolutionary placeholder signalling the transition from dinosaur to bird was Charles Darwin's favourite example.

Over the years, a few brave scientists have gingerly expressed doubts about the theory.

They said Archaeopteryx's bird-like characteristics — feathers, the wishbone, three-fingered hands — were also showing up in proper dinosaurs.

But when they get an idea into their heads, scientists are hard to shift. And all the classic classification signs kept placing Archaeopteryx on the so-called phylogenetic tree showing the shift from dinosaur to bird.

Enter Xing Xu, a professor at Linyi University in China's Shandong Province and discoverer extraordinaire of dinosaur fossils, in particular, a new species unearthed in northern China.

In Liaoning Province, Prof Xu and his team unearthed a dinosaur — Xiaotingia — which was roughly the size of a chicken and weighed less than a kilo.

It shared a host of key characteristics with Archaeopteryx but seemed, at the same time, to fall into another group of non-avian dinos called Deinonychosauria.

A standard computer analysis confirmed as much, but at the same time produced a stunning result — when Xiaotingia is added to the classification table, Archaeopteryx gets reclassified into the same group.

It turns out Archaeopteryx, the iconic 150 million year old "original bird", is probably just another dino with feathers, of which there are many, the researchers said.

It is hard to imagine a tougher fall from evolutionary grace.

"In other words, Archaeopteryx was no longer a bird," Lawrence Witmer, a professor at Ohio university's Heritage College of Osteopathic Medicine, said in a commentary in Nature.

Xiaotingia, it turns out, was the smoking gun that sceptical scientists had been looking for.

Surprised by their findings, Xu and his team ran the analysis again, but this time without the newly discovered species.

Archaeopteryx was restored — in error, they now knew — to its previous perch.

"Perhaps the time has come to finally accept that Archaeopteryx was just another small, feathered, bird-like theropod fluttering around in the Jurassic," Prof Witmer said.

One reason it has been so hard for biologists to embrace this idea may have more to do with history than science.

The first Archaeopteryx specimen was discovered, with uncanny timing, less than two years after the publication of Darwin's game-changing Origin of the Species.

With an evenly matched blend of avian and reptilian features, it became — in textbooks and public debate —"Exhibit A" in explaining the transformative power of natural selection and evolution.

"The familiar fossils have guided almost all scientific thought about the beginnings of birds," Prof Witman said, including himself among those led astray.

Its reclassification, he added, is likely to "rock the palaeontological community for years to come".

So who are the new candidates for king of the roost?

No single species is likely to ever gain the stature that Archaeopteryx once had, Prof Xu said.

But among the new pretenders, three newly discovered creatures stand out — Epidexipteryx, Jeholornis, and Sapeornis.

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